Making tungsten filaments.



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UNITED STATES PATENT OFFICE.

ERNST AEUER, OF BERLIN, GERMANY, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

MAKING TUNGSTEN FILAMENTS.

No Drawing.

To all whom it may concern Be it known that I, Dr. ERNsr AEUER, a subject of the King of Prussia, residing at Berlin, Germany, have invented certain new and useful Improvements in Making Tungsten Filaments, of which the following is a specification.

My invention relates to the manufacture of tungsten filaments, and its object is to facilitate the sintering of the filaments.

Hitherto when making tungsten filaments for electric incandescence lamps it has been customary to make a a yy material with or without an organicor inorganic binder and to pres filaments f r qm the mass or to son ire-earnest" i aw filainents the is removed, and if tungsten c omppg ds has been taken raw m l sary to reducetli'ecompounds. Besides, the filaments m st be sintened which may be performed immediate y after the just mentioned processes and jointly with them or separately. Filaments produced in this way are inferior to drawn metal filaments as regards mechanical qualities. This may be explained by the supposition, that the smallest particles of a drawn metal wire are in such degree intimately connected one with another by the melting processes passed by the metal before being drawn to wire, as it never can be attained by the paste-processes. Besides, if the paste has been made with a binder, the latter being driven out before or during the sintering breaks up the structure of the pressed filament in such degree, that the metal particles, which are to be sintered, are in a relatively loose connection and that, therefor, the sintering of the single particles materially is rendered more difficult.

The last mentioned inconvenience is especially marked, if the sintering of the filaments is not effected by current introduced into them, but is achieved in an electric furnace in an atmosphere of hydrogen, for example in a carbon tube furnace, into which the filaments are brought on supports of oXid of thorium. In this case when sintering it is not possible to raise the temperature as high, as if the filaments are sintered by current flowing through them, as the furnace, then, would deteriorate too rapidly and must be renewed very frequently.

The invention purposes to facilitate the Specification of Letters Patent.

Application filed August 10, 1910.

it is also neces' Patented J ully 18, 1916.

Serial No. 576,522.

sintering of the filaments by a preparatory treatment in order that it may be attained in an electric furnace in an atmosphere of hydrogen without endangering the furnace too much. For this purpose the tungstenifer; ou filanien ts are s bjeeted before the s intera chemical reaction, which brings the separate molecules in connection by glow ing the filamg or in another gas contain g j l or in such a I W w imam-u ma .W-i gas mixture at a relative y ow temperature and by converting them, thereby, into a nitrogen compound. The filaments must be heated to at least noticeable red-heat, it is advisable to employ a temperature of "('00900 centigrade. By the following heating up to bright incandescence which is to be performed in order to sinter tl1e filaments in the furnace in an osphere of hydrogen the nitrogen compound is decomment is especially a mixture of ammoniagas and hydrogen or of nitrogen and hydrogen. If the trioxid of tungsten or other oxygen compounds have been taken, as raw material, by the glowing in the just mentioned gases the reduction of the oxygen compound may be effected, too. The elimination of the binder or of the carbon left in the filament from the binder may also be joined with the described heating process in the gas containing nitrogen by first raising the temperature as high, as is necessary for the elimination of the carbon, and then lowering the temperature to about 700900 centigrade. It is however equally possible to remove the binder or its carbon earlier or later.

The conversion of the filaments in the nitrogen compound may be effected wholly or partly. As trials show, by the described processes the later sintering is facilitated and filaments of greater mechanical strength are produced.

One could mind to perform the sintering, too, in the above mentioned gas or gas mixture instead of in hydrogen by raising the temperature up to bright incandescence after the formation of the nitrogen compound. This is however not practical, as at the high temperature the nitrogen of the gas attacks the carbon tube of the furnace with production of cyanogen, whereby the persons charged with the performance of the processes would easily be exposed to dangers. Even with the employment of a furnace consisting of a high melting metal inconvenience would result, as the ammonia-gas would diffuse in the outer room through the metal tube. On' the other hand it is not practical to perform the preparatory treatment above described in such a mixture of hydrogen and nitrogen or hydrogen and ammonia'gas, which is poor in nitrogen, as in this case the conversion of the filaments in the nitrogen compound would require a long time. From this it may be seen how advantageous it is to employ two different gases, viz. a gas rich in nitrogen during the preparatory treatment and hydrogen during the sintering.

lVhat I claim as new and desire to secure by Letters Patent of the United States, is 1. The method of manufacturing tungsten filaments which consists in heating a filament comprising an oxygen compound of tungsten in an atmosphere rich in nitrogen to a temperature at which said filament is converted into a nitrogen compound and then decomposing said compound by heating to a materially higher temperature in hydrogen, to decompose the nitrogen compound and sinter the resulting tungsten metal.

2. The method of manufacturing tungsten filaments which consists in converting filaments comprising an oxygen compound of tungsten into a nitrogen compound of tungsten by heating the same in a nitrogencontaining gas to a temperature of about 700 to 900 0., and then heating said filaments by radiant heat to a temperature of bright incandescence 1n hydrogen to decom pose the nitrogen compound and smter the.

DR. ERNST AEUER.

Vitnesses JULIUS RUMLAND, OSKAR SINGER.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. 0. 

